Ohm's Law and Power

This is the core quick card for voltage, current, resistance, and power. Use it for wire sizing, fuse planning, current-draw sanity checks, and fast electrical math during design or troubleshooting.

Tiny Version

Voltage is push, current is flow, and resistance is squeeze. Power tells you how hard the electrical system is actually working.

Builder Version

Use this page when you need to estimate amplifier current draw, choose a believable starting wire size, or sanity-check whether a fuse and wire plan makes sense before the install goes live.

Ohm's law reference diagram showing voltage at the top of a triangle, current and resistance at the base, plus matching power formulas for quick calculations — The triangle is a memory shortcut: cover the value you want, then use the remaining positions to remember whether to multiply or divide.

Core Formulas

V = I x R
I = V / R
R = V / I

P = V x I
P = I^2 x R
P = V^2 / R

What The Letters Mean In Real Life

V - voltage, the electrical push from the source.
I - current, how much electrical flow the load is asking for.
R - resistance, how much the load pushes back against flow.
P - power, the rate at which energy is being delivered.

Worked Example: How Much Current Will A 500 W Amp Ask For?

P_input = P_output / efficiency = 500 / 0.85 = 588 W
I = P / V = 588 / 12 = 49 A continuous
I_design = 49 x 1.25 = 61 A

That makes 6 AWG wire and an 80 A fuse a believable starting example, not a universal answer for every install.

Common Mistakes

Gain is not power. Turning gain up does not magically create clean output.
Power ratings and actual current draw are not the same thing all the time.
Final wire and fuse choices still have to respect real run length, hardware guidance, and the actual vehicle electrical system.